1. Field of the Invention
The present invention relates to a knocking detection apparatus and detection method that detect, with high precision, the presence of knocking and the timing thereof from changes in ion currents that are detected using spark plugs at the time of combustion of an internal combustion engine.
2. Description of the Related Art
It is known that ions are generated when fuel is combusted inside the cylinders of an internal combustion engine and that these ions can be measured as ion currents by disposing probes that apply a high voltage inside of the cylinders. Because knocking vibration components are superposed on the ion currents when knocking occurs in an internal combustion engine, the occurrence of knocking can be detected by detecting these vibration components. However, spark noise includes many frequency components superposed on the ion currents, end up being detected as vibration components of knocking, and are mistakenly determined to be knocking even if knocking is not actually occurring.
The following technologies have been disclosed as technologies to avoid this drawback. First, the technology disclosed in Japanese Patent No. 3184451 (pp. 2–3, FIGS. 1 and 2) (Japanese Published Patent Application 9-228941) includes a bandpass filter that filters only the knocking frequency components superposed on the ion currents when knocking has occurred and a noise bandpass filter that allows frequency components different from the knocking frequency components to pass. For example, by blocking noise resulting from the operation of an injector, when detected through the noise bandpass filter, using a switch, a knocking signal is not input to a determination circuit.
In the technology disclosed in JP-A-11-2175 (pp. 3–4, FIGS. 1 and 3), signals based on the ion currents pass through a high-pass filter, and knocking signals pass through a filter allowing a specific frequency band to pass. Only the noise component is separately retrieved, using the filter obstructing the specific frequency band, the peaks of both are respectively held, digitally converted, and imported to control means. Both signals are compared by the control means, and it is determined whether knocking is occurring from the compared signals.
Moreover, in JP-A-61-57830 (pp. 3–4, FIGS. 1 and 3) signals obtained through a filter selectively passing knocking signals based on the ion currents and a filter selectively passing unique vibration frequencies generated by the mechanical dimensions of each cylinder are respectively integrated over a predetermined period. Signals indicating the occurrence of knocking are obtained from the ratio of the respective integrated values. The signals are integrated during a predetermined number of revolutions, whereby knocking is detected.
Moreover, in JP-A-11-295188 (pp. 5–8, FIGS. 9 to 11) signals based on the ion currents are passed through a high-pass filter and a low-pass filter, whereby only a knocking detection signal is extracted. The knocking detection signal is A/D converted, and a discrete Fourier transform is applied. The resulting frequencies are analyzed to determine whether the signal results from knocking or from noise, and the running state of the internal combustion engine is determined.
As described above, these various technologies have been disclosed. However, in the case of Japanese Patent No. 3184451, even if a signal including the knocking component is detected, it is determined to be invalid if a signal including spark noise is included, and it is mistakenly determined that knocking is not occurring even if knocking is occurring. Also, the ion currents are signals that are small, depending on the running state, and the noise signal becomes large when the operating noise of the injector and external noise, such as from a phone are superposed, so that knocking cannot be completely detected with the methods of JP-A-11-2175 and JP-A-61-57830.
Also, the prior art uses, as the detection target, time intervals between each ignition as units in relation to knocking detection. Use of these time intervals cannot accurately detect knocking, because knocking appears and disappears in units of time shorter than these time intervals. For this reason, there has been the problem that control methods cannot be made to correspond to the timing of knocking occurrence. Moreover, there have been problems. The resistance of the determination function, with respect to ion current signals whose amplitude has been increased due to the influence of additives added to the fuel, is low. The ion currents have superposed impulse noise including many frequency components. Also, in all of the prior examples, knocking determination precision has been low because the time resolution has been low.